Process of making and utilizing sheeted adhesives and the products thus produced



Patented May 22;;119342 UNITED STATES PROCESS OF MAKING AND UTILIZINGSHEETED ADHESIVES AND' THE PROD- ,.UCTS THUS PRODUCED Josef Weber andFranz Hengstebeck, Essen- Ru'hrgGermany, assignors, by mesne assignments, to Th. Goldschmidt Corporation, New York, N. Y., a corporation ofDelaware No Drawing. Application June 2, 1931, Serial No.

541,734. In Germany February 2, 1929 7 Claims.

This invention relates-to processes of making and utilizing sheetedadhesives and to products thus obtained; and it comprises as a newadhesive articlea substantially dry, substantially homogeneous, thinflexible sheet of an alkaline con-- densation product of formaldehydewith a phenol, said sheet ordinarily containing a tenuousfiberreinforcement and said product being solid at ordinary temperature;becoming plastic and melt- I 0 ing when, warmed and setting to a hardpermanent infusible form at temperatures somewhat above 100 0.; auditalsocomprises processes of making said adhesive articles and it furthercomprises methods of utilizing said new adhesive article and products soobtained; all as more fully hereinafter set forth and as claimed.

In the usual method of cementing wood to wood, including afiixingveneers-and making plywood,

the surfaces are treated with a solution, of glue 0 and settingperformed under heat and pressure;

Setting is really a removal of water and where extensive surfaces areunited, the water is taken up by the wood. Most liquid glues containlarge proportions of water and in making plywood,.the

amount of water to be dissipated in the glue used may be as high as toper cent of the weight of the wood to be joined. In building up plywoodassemblages, the glue is applied toinner layers and the water is takenup by proximate 30 layers thereby necessarily swelling these. At thisstage in the operation the product includes a.

swollen inner wood layer connected to lessmoist outer layers or plies.In drying, the swollen inner layers tend to shrink to their originalproportions thereby setting up heavy stresses and causing warping.Making plywood in this manner by the assemblage of successive laminae ofwood with intermediate drying is a tedious operation and the product isapt to be irregular. The whole assemblage must be finally dried andunless this. final drying, as well as the intermediate dryings, beconducted with-exceptional care and skiilan unsatisfactory productresults. It maybe warped, mottled or exhibit fissuresiincipientcleavage). In order to obviate these diiiiculties it hasbeen proposed tomanufacture. plywood and afiix veneers by employing between the layersof wood a cementing layer in the form of glue-surfaced sheets of paper,of fabric, or even of wood. In making the cementing layer, suitablesheets are passed through a glue solution and afterwardsdricd so as toform adhesive surfaced sheets adapted to be interposed between the woodplies. Using sheets of this character the amount of water necessary canbe limited to that required to make the surface of the sheets sticky;and this is an advantage. This method while better, than the more commonprocedure of cementing by liquid glue directly applied is neverthelessopen to certain objections. For one thing in the final product, there isanintermediate structural element between the wood plies. Foranothenply-e.

wood made in this manner when subjected to changes in temperature andmoisture conditions frequentlytends to split apart along the plane ofthe intermediatefabric layer; the layer. carrying the glue on itssurfaces. Unless the glue is waterproofed in some manner, the.driedlayer is not resistant to the action of moisture.

In afiix'ingveneers and in making plywood it is desirable to havethewood layers as close together, face to face, as possible, restrictingthe amount of intermediate adhesive to that sum-,- cient to even outsurface irregularities. And it is desirable to have an adhesive.requiring in setting the dissipationofno great amountof water or of avolatile solvent; of any amount causing substantial swelling in thewood. These results are accomplished in the present invention where- Vin is provided a thinsubstantially dry, substantially homogeneous laminaof adhesive usually containing a tenuous fiberreinforcement innegligible amount; the adhesive being .solid at the ordinarytemperatureQsoftening andfusing to a mobile liquid at highertemperatures and finally setting to a hard infusible, permanent form onexposureto temperatures such. as are used .in making plywood, say at 130Ca For our purpose we use a particular condensation product of a phenoland formaldehyde in the presence of a rather large amount of alkali;this alkali serving both as a catalyst in inducing condensationandhaving Icertain otherfui'iticns. As the phenol, ordinary'phenol may beused or one ofthe cresols. In'lieu of formaldehyde, acetaldehyde orother aldehydes may be employed. However, ordinary phenol and ordinaryformaldehyde, as the commercial 40 per cent solution, givegood results.On dissolving equivalent amounts of phenol and formaldehyde (insolutionlin 40 per cent caustic soda lye using the amount of lyenecessary for solution, a satisfactory,preparation can be made-for thepresent purposes. With a batch of 94 kilograms of phenol and 100kilograms of commercial 30per cent formaldehyde solution about 17kilograms of 40 per cent NaOH solution give a good -preparation. Thisliquid is 'kept' warm. for a time say at 80 C. for 1% hours, withconstant stirring until an easy flowing oily dark liquid is obtained.

Heating must be stopped before an aqueous layer separates from thereaction products. The separation of such a layer 'shows that thereaction has gone, too far and the condensation product obtained willnot possess the advanta geous properties here desired. The viscosity ofthe product obtained depends upon the time of heating but is rather lowin any event. The exact viscosity desired can be obtained byinterrupting the heating and then cooling. Because of the solventinfiuence of the excess of alkali and of the water present, noseparationinto two layers is produced. The oily liquid can be dried to asubstantially dry material at temperatures below about 100 C. withoutgoing into the final insoluble resin. Ordinarily it is desired to drythe material to about 2 per cent water. By proper manipulation the driedmaterial may be made in thin sheets. These sheets at the ordinarytemperature are not tacky but are somewhat hygroscopic in the sense thatthey will take up morev water from the air. Ordinarily the amounttakenup will give a final product of'about 5 to 8 per cent; this varying withthe humidity. With this content of water the product is flexible and notsticky or tacky andthe sheets can be packaged, shipped and stored asrolls without danger of adhesion.

As so far described, the sheets are made without the use of areinforcement but for manufacturing reasons it is better to employ atenuous reinforcement of fiber in negligible amount; an amountinsufficient to produce a substantial intervening layer between thesheets of wood ultimately to be united. As'this'reinforcement we employan open textured, thin paper, or like sheeted material. With the aid ofthis paper it is possible to produce the present material by ordinarymanufacturing operation in a continuous manner; a web of paper passingfirst through the initial condensation product,'past equalizing rolls.and then through drying apparatus. Drying is usually so conducted as togive about 2 per cent water in the dry material and sufficient exposureto air is then permitted to allow assumption of the full amount of waterof condition; usually about 8 per cent. The proportion of fiber toadhesive varies but is usually in about the ratio of 1 2. With thin opentextured'pa'per in this proportion the final sheeted product has asubstantially continuous body of adhesive. In making such completely anduniformly impregnated sheets which are in fact continuous films ofadhesive, the thickness and porosit'yor open texture of the reinforcingsheet are so correlated with the liquidity or'yiscosity of the oilyliquid condensation product containing caustic soda as to insurea-complete, continuous and uniform impregnation. When this relation isproperly established the oily liquid penetrates all the poresof thereinforcing medium and .it is only necessary to apply the proper amountof liquid to "give the is not tacky; is not hygroscopic enough to becomemoist and sticky in ordinary air. It does however take up a littlewaterof condition; enough to make it flexible and easily handled. The drycomposition on warming to a few degrees above the ordinary temperaturebecomes plastic enough to facilitate easy sheeting and on recooling ispermanent; it can be stored, packaged and handled without trouble. Inheating to fusion in .use, probably the caustic soda and the smallreaches a point somewhere around 130 C. when the catalytic actionbecomes extremely rapid. In the. final product the caustic soda does notexist in any form making the article hygroscopic;

nor is it necessary in making plywood to provide for the dissipation ofthe water present in the mixture. It is, in any event, small in amountbeing only about 5 to 8 per cent of the adhesive.

When the fiexible sheeted adhesive (with or without reinforcement) isplaced between two layers of wood in the usual way of aflixing veneersormaking plywood and heat and pressure are applied, the adhesiveat firstyields and softens. then fuses and is then taken up for the most part bythe pores of the wood; finally solidifying in place. With about '8percent water in tlie material on fusing it forms afairly mobile liquidreadily taken up by pores as a whole; there without much change involume and with very little extrication of water; not enough to causeswelling or require any special care in subsequent drying.

Because of the propertiesof the present adhesive sheet it is possible tojoin a number oi. layers of plywood. together simultaneously instead ofsuccessively as is the usual practice; thereby economizing time andlabor.

While the invention'has been particularly described in its use incementing veneers and making plywood, the adhesive sheets of the presentinvention are advantageous in manyother relations and may beused forgeneral cementing purpose. Their use in forming a. facing layer onvarious articles is advantageous.

What we claim is:

1. As a new product, adhesive papers for plywood manufacture comprisinga porous open textured tissue paper sheet impregnated with an initialcondensation product of an aldehyde with a phenol, said condensationproduct containing a. substantial amount of alkali, being capable ofsoftening and fusing under heat and pressure to give a mobile liquid,being capable of hardening under said heat and pressure to give ahardened insoluble body, and having been produced at low temperatures ina dilute causticalkali solution without separation of an aqueous layer.

2. As a new product, adhesive papers for plywood manufacture comprisinga porous open textured thin tissue paper sheet impregnated with a. lowtemperature, initial condensation product of an aldehyde with a phenol,caustic soda, and a small amount of water fixed as water of condition,said water being about 8 per cent of the total adhesive, the ratio ofsaid condensation product to the paper being about 2:1.

3. A process of making adhesive papers for plywood manufacture whichcomprises heating formaldehyde with a phenol in an aqueous solution ofcaustic alkali under conditions suitable for producing a homogeneous,easy flowing, oily in itial condensation product without the separationof an aqueous'layer, impregnating a porous, open textured tissue papersheet with said product without the presence of extraneous solvents anddrying to produce a non-tacky surface.

4. In the making of adhesive papers for plywood manufacture, the processwhich comprises warming a phenol and formaldehyde together in thepresence of an aqueous caustic soda solution under conditions suitablefor producing a homogeneous oily, liquid condensation product withoutthe separation of an aqueous layer, and impregnating a porous, opentextured, thin tissue paper sheet with said product and drying the impregnated paper, thevamount of alkali present not being suiiicient togive the dried sheet a tacky surface but being suflicient to causeabsorption of from about 5 to 8 percent of water of condition onexposure to air.

5. In the making of adhesive papers for plywood manufacture, the processwhich comprises reacting together an aldehyde and a phenol in an aqueoussolution of caustic alkali under conditions suitable for producing ahomogeneous, oily, liquid, initial condensation product withoutseparation of an aqueous layer, impregnating a porous, thin tissue papersheet with said prodnot and drying the impregnated sheet at temperaturesbelow about 100 C. to form a substantially dry, solid but flexible sheetcontaining a substantial amount of caustic soda and water of condition;the impregnating condensation product being capable of assuming a highlyfluid state under heat and pressure at temperatures not substantiallyabove 130 C.

6. As a new product, an adhesive sheetlfor plywood manufacturecomprising a porous, open textured, tissue paper sheet impregnated withan initial condensation product of an aldehyde with a phenol, formedwithout separation of an aqueous layer and in the presence of a causticsoda solution, and containing a small amount of water fixed as a waterof condition, said water being about 5 to 8 per cent of the totaladhesive; the said condensation'product being free from extraneoussolvents, being capable of assuming a highly fluid state under heat andpressure at temperatures not substantially above 130 C. and, when placedbetween sheets of plywood and subjected to heat and pressure, beingcapable of fusing to form a mobile liquid and then hardening in situ tounite said sheets with a hard, insoluble bond.

7. As a new product an adhesive sheet for plywood manufacture comprisinga porous, open textured, thin tissue paper sheet impregnated with alow-temperature, initial condensation product of an aldehyde with aphenol formed in the presence of a caustic alkali solution, the saidcondensation product being free from extraneous solvents, being capableof assuming a highly fluid state under heat and pressure at temperaturesnot substantially above 130 C. and, when placed between sheets ofplywood and subjected to heat and pressure, being capable of fusing toform a mobile liquid and then hardening in situ to unite said sheetswith a hard, insoluble bond.

JOSEF WEBER. FRANZ HENGSTEBECK.

